The excellent series of special reports on controversies in neuroradiology included that of Bryan, Rigamonti, and Mathis on the treatment of acutely ruptured cerebral aneurysms (1). These authors deftly picked their way through the dilemmas currently facing us in selecting patients for endovascular treatment. Confining themselves to a discussion of the use of the Guglielmi detachable coil (GDC), they suggest that the efficacy of coils to pack aneurysms now has been resolved by published reports of the device's clinical performance and the approval of GDCs by the Food and Drug Administration (FDA). They attribute current uncertainties to a lack of published data regarding outcomes of GDC packing as compared to conventional neurosurgical clipping.

The authors make only the briefest reference to the uncertainty that remains concerning the long-term biological response to coils that is fundamental to the efficacy of this form of treatment. It is a remarkable fact that the FDA approved GDCs for clinical use in 1995, though very little was known about the cellular response to this implant. The published studies at the time consisted of reports of the device's use in experimental animal models (eg, in dogs, rabbits, and pigs) and a single, postmortem report (2). The FDA presumably based their approval on the excellent safety record of platinum for other human implants. The results of subsequent studies of the cellular response to GDCs in experimental aneurysms are conflcting (3, 4), and substantial human histologic data are still lacking.

It is intuitive that the long-term safety of this type of embolization depends on the formation of stable fibrosis around the coils. We know that aneurysms treated with GDCs are liable to regrow, and that this tendency is proportional to the extent to which coils continue to be exposed to arterial blood flow. What remains unknown is how long it takes, if ever, for the coil-thrombosis complex to become completely stable. We, therefore, need studies to monitor the efficacy of endovascular therapy in order to answer the patient who asks, “Will the aneurysm ever bleed again?”